The present invention relates to an angular velocity modulating device having elemental units each including mechanical gear means for obtaining an automatic stepless transmission mechanism usable in power drive means generally.
A typical example of a conventional mechanical automatic transmission mechanism using gears is disclosed in Japanese Patent Publication No. 42181/1984, construction of which is used in this application as FIG. 1 to show the state of art, in which a reference numeral 301 depicts a first common shaft on which a first non-circular drive gear 303 is fixedly mounted. A second non-circular drive gear 305 is rotatably supported by the common shaft 301. The second drive gear 305 meshes with a second non-circular driven gear 309 rotatably supported by a second common shaft and the first drive gear 303 meshes with a first non-circular driven gear 307 rotatably supported by the second common shaft 312.
The second drive gear 305 is angularly shiftable to an arbitrary angular position with respect to the first drive gear by means of a control device composed of the movable element 304, a fixed element 302 fixedly secured to the common shaft 301 and a regulating device 306.
Differential bevel gears 308 and 310 are fixedly mounted on the first and second driven gears 307 and 309, respectively, the bevel gears being meshed with a pinion gear 313. The pinion gear 313 is mounted, by a nut 314, on a differential element 311 fixedly secured to the common shaft 312.
FIG. 2 illustrates an example of the paired non-circular drive and driven gears 303 and 307 and FIG. 3 is a graph showing an angular velocity ratio given to the paired gears with concrete numerical values selected as an example. In FIG. 3, abscissa is scaled with angular shift .theta. of the drive gear and ordinate is scaled with angular velocity ratio R where R=(angular velocity of the driven gear)/(angular velocity of the drive gear).
FIGS. 4 to 6 are graphs showing characteristics of the conventional elemental units having different angular velocity ratios, respectively, abscissa and ordinate thereof being scaled as in FIG. 3.
In such conventional device, it is possible to establish conditions in which angular velocity ratio R becomes constant at least successibly and to continuously control a magnitude of R. The control of the angular velocity ratio R is performed by varying a relative deviation of angular position between the first and second drive gears 303 and 305 (this is referred to as "phase deviation" hereinafter) by means of the above mentioned control device. When the phase deviation is 180.degree., the angular velocity transmitted through the differential device to the second common shaft 312 is always equal to that of the first common shaft 301 and thus the angular velocity ratio R is unity constantly as shown in FIG. 4.
When the deviation is larger or smaller than 180.degree., a sequence of a region a in which the angular velocity ratio is larger than unity constantly, a region b in which R decreases, a region c in which R is smaller than unity constantly and a region d in which R increases appears repeatingly as shown in FIGS. 5 and 6. The values of R in the regions a and c vary in correlation to the phase deviation.
Therefore, by using a plurality of such units so that the regions a and c are connected, i.e., the regions b and d are eliminated, it is possible to constitute a stepless transmission. However, since such unit requires a total of 7 gears, 4 on non-circular gears and 3 of bevel gears, the number of fundamental elements of the unit becomes at least ten. Thus, when such stepless transmission be constituted with such units, the number of mechanical elements thereof becomes very large.
It has been known generally that the friction type power transmission is featured by a smooth transmission of rotation and that the non-friction type such as using gears is featured by a high transmission efficiency.
Comparing them in view of application thereof to the conventional stepless transmission, the friction type has a problem of power loss due to slippages between contact portions thereof while the non-friction type has a problem of complicated construction as mentioned above.
The advantage of the high transmission efficiency of the non-friction type transmission tends to be lost due to inertia of the mechanical elements and frictions between them.